The supermassive black hole at the centre of our galaxy is, for now, only scientific theory, but several celestial bodies in the centre are orbiting nothing – apparently – at thousands of miles per second.2. The numbers game
Strictly speaking, there are currently 14 confirmed black holes, the closest being Cygnus X-1 which is around 8,000 light years from Earth.3. Compression
Theoretically, anything can become a black hole as long as it is compressed to zero volume and yield infinite density (known as the Schwarzschild radius).4. Dog eat dog
What happens when two black holes collide? Most believe that the one with the bigger gravitational force will suck up the other, creating an even bigger black hole.5. In the middle
At the centre of a black hole reality becomes warped as matter is crushed to infinite density, so essentially space and time as we know them cease to exist.